Compensating for radiation pattern in radio system, and radio system

ABSTRACT

The invention relates to compensation of a radiation pattern tern in a radio system. The solution comprises forming a primary radiation pattern by weighting signals of antenna branches with primary weights. The primary radiation pattern is compensated with a compensating radiation pattern after one or more antenna branches have been disconnected. The solution enables operation of the radio system without interruptions in certain fault situations of the base station.

FIELD

The invention relates to a method of compensating for a radiationpattern in a base station of a radio system and to a radio systemimplementing the method.

BACKGROUND

As wireless data transmission will become more common in the future andthe number of users will grow, it is essentially important to increasethe capacity of systems by improving their performance. One way ofenhancing the performance of a radio system is to use radiation patternsin the transmission and reception of a base station that have beendesigned for the base station environment according to the need for datatransmission capacity and that are typically formed by means of anantenna configuration consisting of one or more antenna elements byweighting signals of different antenna branches. The radiation patternstypically comprise two or more beams which can be associated withbeam-specific coding. In an ideal case, each beam thus enables aseparate physical radio channel, which reduces the multi-useinterference that impairs the performance of the radio system. Theproperties of the radiation pattern are sensitive to changes in antennabranches caused by interference in the supply electronics of the antennaelements, for example.

In a prior art solution, the interference in the antenna branches areeliminated by service personnel dispatched to the scene.

One problem associated with the prior art solution is that there is adelay between interference at a base station and elimination of thisinterference. In that case the base station may function with adeficient radiation pattern for a long time, which may increase themulti-use interference and drastically reduce the performance of theradio system.

BRIEF DESCRIPTION

An object of the invention is to provide an improved method ofcompensating for a radiation pattern in a radio system, the methodcomprising: forming a primary radiation pattern by weighting signals ofat least two functional antenna branches of a base station. The methodis characterized by disconnecting at least one antenna branch andforming a radiation pattern which compensates for the primary radiationpattern by weighting signals of the functional antenna branches.

Another object of the invention is to provide an improved method ofweighting signals in a radio system, the method comprising: weightingsignals of at least two functional antenna branches of a base stationwith primary weights to form a primary radiation pattern. The method ischaracterized by disconnecting at least one antenna branch and weightingsignals of the functional antenna branches with weights which compensatefor the primary weights to form a compensating radiation pattern.

A further object of the invention is to provide an improved radio systemcomprising: a base station for forming a radio interface of the radiosystem; the base station comprises at least two antenna branches forestablishing a radio link to terminals; each antenna branch comprises atleast one antenna element for forming an antenna array; and the basestation comprises means for weighting signals of the functional antennabranches to form a primary radiation pattern. The radio system ischaracterized in that the base station is arranged to disconnect atleast one antenna branch and the weighting means are arranged to weightsignals of the functional antenna branches to form a radiation patternwhich compensates for the primary radiation pattern.

The invention is based on the idea that when interference occurs in anantenna branch, this antenna branch is disconnected and signals of theremaining antenna branches are weighted so that the resulting radiationpattern replaces the original radiation pattern.

One feature of the invention is that the radio system remains functionaleven in an interference situation. Another feature of the invention isthat it can be implemented by software.

LIST OF FIGURES

The invention will now be described in greater detail by means ofpreferred embodiments with reference to the accompanying drawings, inwhich

FIG. 1 is a simplified block diagram of the structure of atelecommunications system,

FIG. 2 is a second simplified block diagram illustrating the structureof a telecommunications system,

FIG. 3 is a block diagram illustrating blocks of a base station,

FIG. 4 is a block diagram illustrating the present solution,

FIG. 5 illustrates an example of a radiation pattern formed by the basestation,

FIG. 6 illustrates a second example of a radiation pattern formed by thebase station, and

FIG. 7 illustrates a third example of a radiation pattern formed by thebase station.

DESCRIPTION OF THE EMBODIMENTS

The embodiments described are applicable to telecommunications systems.An example of such telecommunications systems is the wide-band WCDMAradio system that utilizes spread-spectrum data transmission. In thefollowing, embodiments will be described using GSM/GPRS and UMTS radiosystems as examples without limiting the invention to these systems, asis obvious to a person skilled in the art.

FIG. 1 illustrates the structure of radio systems in a simplified manneron the level of network elements. The structure and functions of thenetwork elements are illustrated rather cursorily since they are knownper se. The radio-independent layer of the telecommunications system isrepresented by a core network CN 100. Radio systems are illustrated by afirst radio system, i.e. a radio access network UTRAN 130, and a secondradio system, i.e. a base station system BSS 160. The term ‘UTRAN’ is anabbreviation from UMTS (Universal Mobile Telephone System) TerrestrialRadio Access Network, i.e. the radio access network 130 is implementedby the wideband code division multiple access technique (WCDMA). Thefigure also shows user equipment UE 170. The base station system 160 isimplemented by the time division multiple access technique (TDMA).

On a general level, the radio system can also be defined to compriseuser equipment, which is also known. as a subscriber terminal or amobile phone, for instance, and a network part, which comprises thefixed infrastructure of the radio system, i.e. the core network, radioaccess network and base station system.

The structure of the core network 100 corresponds to a combinedstructure of the GSM (Global System for Mobile Communication) and GPRS(General Packet Radio Service) systems. The GSM network elements areresponsible for establishing circuit-switched connections, and the GPRSnetwork elements are responsible for establishing packet-switchedconnections; some of the network elements are, however, included in bothsystems.

A mobile services switching centre (MSC) 102 is the centre point of thecircuit-switched side of the core network 100. The same mobile servicesswitching centre 102 can be used to serve the connections of both theradio access network 130 and the base station system 160. The tasks ofthe mobile services switching centre 102 include: switching, paging,user equipment location registration, handover management, collection ofsubscriber billing information, encryption parameter management,frequency allocation management, and echo cancellation. The number ofmobile services switching centres 102 may vary: a small network operatormay only have one mobile services switching centre 102 but large corenetworks 100 may have several ones.

Large core networks 100 may have a separate gateway mobile servicesswitching centre (GMSC) 110, which is responsible for circuit-switchedconnections between the core network 100 and external networks 180. Thegateway mobile services switching centre 110 is located between themobile services switching centres 102, 106 and the external networks180. The external network 180 can be for instance a public land mobilenetwork (PLMN) or a public switched telephone network (PSTN).

A home location register (HLR) 114 comprises a permanent subscriberscriber register, i.e. the following information, for instance: aninternational mobile subscriber identity (IMSI), a mobile subscriberISDN number (MSISDN), an authentication key, and when the radio systemsupports GPRS, a packet data protocol (PDP) address.

A visitor location register (VLR) 104 contains roaming information onuser equipment 170 in the area of the mobile services switching centre102. The visitor location register 104 comprises almost the sameinformation as the home location register 114, but in the visitorlocation register 104, the information is kept only temporarily.

An equipment identity register (El R) 112 comprises the internationalmobile equipment identities (IMEI) of the user equipment 170 used in theradio system, and a ‘white list’, and possibly a ‘black list’ and a‘grey list’.

An authentication centre (AuC) 116 is always physically located in thesame place as the home location register 114, and it comprises asubscriber authentication key Ki and a corresponding IMSI.

The network elements shown in FIG. 1 are functional entities whosephysical implementation may vary. Usually, the mobile services switchingcentre 102 and the visitor location register 104 constitute one physicaldevice while the home location register 114, equipment identity register112 and the authentication centre 116 constitute another physicaldevice.

A serving GPRS support node (SGSN) 118 is the centre point of thepacket-switched side of the core network 100. The main task of theserving GPRS support node 118 is to transmit and receive packetstogether with the user equipment 170 supporting packet-switchedtransmission by using the radio access network 130 or the base stationsystem 160. The serving GPRS support node 118 contains subscriber andlocation information related to the user equipment 170.

A gateway GPRS support node (GGSN) 120 is the packet-switched sidecounterpart to the gateway mobile services switching centre 110 of thecircuit-switched side with the exception, however, that the gateway GPRSsupport node 120 must also be capable of routing traffic from the corenetwork 100 to external networks 182, whereas the gateway mobileservices switching centre 110 only routes incoming traffic. In ourexample, external networks 182 are represented by the Internet.

The first radio system, i.e. the radio access network 130, consists ofradio network subsystems RNS 140, 150. Each radio network subsystem 140,150 consists of radio network controllers RNC 146, 156 and B nodes 142,144, 152, 154. Since the B node is rather an abstract concept, the termbase station, to which the B node corresponds, is frequently usedinstead.

The radio network controller 146 controls the B nodes 142, 144 belongingto it. In principle, the devices implementing the radio path and theirfunctions should be in B nodes 142, 144 while the control devices shouldbe in the radio network controller 146.

The radio network controller 146 is responsible for the following tasks,for instance: radio resource management of the B node 142, 144, intercell handovers, frequency management, i.e. allocation of frequencies tothe B nodes 142, 144, management of frequency hopping sequences,measurement of time delays on the uplink, implementation of theoperation and maintenance interface, and power control.

The B node 142, 144 includes at least one transceiver for implementingthe WCDMA radio interface. Typically, the B node serves one cell, butalso a solution where one B node serves several sectored cells isfeasible. The diameter of a cell may range between a few meters anddozens of kilometers. The tasks of the B node 142, 144 include:calculation of timing advance (TA), uplink measurements, channel coding,encryption, decryption, and frequency hopping.

The second radio system, i.e. the base station system 160, consists of abase station controller BSC 166 and base transceiver stations BTS 162,164. The base station controller 166 controls the base transceiverstations 162, 164. In principle, the devices implementing the radio pathand their functions should be included in the base stations 162, 164,while the control devices should be included in the base stationcontroller 166. The base station controller 166 is responsible forsubstantially the same tasks as the radio network controller 146.

The base station 162, 164 includes at least one radio transceiver whereeach carrier has eight time slots, i.e. the transceiver establisheseight physical channels on each carrier. Typically, one base transceiverstation 162, 164 serves one cell, but also a solution where one basetransceiver station 162, 164 serves several sectored cells is feasible.The base transceiver station 162, 164 also comprises a transcoder forconverting the speech coding format used in the radio system to thatused in the public switched telephone network. In practice, however, thetranscoder is physically located in the mobile services switching centre102. The base transceiver station 162, 164 has the same tasks as the Bnode.

The subscriber terminal 170 consists of two parts: mobile equipment (ME)172 and a UMTS subscriber identity module (USIM) 174. The USIM 174includes information on the user and particularly on data security, e.g.an encryption algorithm. The subscriber terminal 170 comprises at leastone transceiver for establishing a radio link to the radio accessnetwork 130 or base station system 160. The subscriber terminal 170 maycomprise at least two different subscriber identity modules. Thesubscriber terminal 170 further comprises an antenna, a user interfaceand a battery.

The description shown in FIG. 1 is rather general, so FIG. 2 shows amore detailed example of a cellular radio system. FIG. 2 comprises onlythe most essential blocks, but it is obvious to one skilled in the artthat a conventional cellular radio network also comprises otherfunctions and structures that need not be explained in closer detailhere. The details of a cellular radio system may differ from those shownin FIG. 2, but these differences are irrelevant to the invention.

FIG. 2 shows a mobile services switching centre 106, a gateway mobileservices switching centre 110, which is responsible for the connectionsof the mobile communication system to the external world, here to thepublic telephone network 180, and a network part 200 and terminals 170.

The network part 200 of the cellular radio network comprises basetransceiver stations 204. A base transceiver station corresponds to anode B 142, 144 of FIG. 1. Several base transceiver stations 204 arecontrolled in a centralized manner by a radio network controller 146communicating with the base transceiver stations and comprising a groupswitching field 220 and a control unit 222. The group switching field220 is used for switching speech and data and for connecting signallingcircuits. The control unit 222 carries out call controlling, mobilitymanagement, collection of statistics, signalling and control andmanagement of resources.

The base transceiver station 204 and the radio network controller 146constitute a radio network subsystem 140, which further comprises atranscoder 226, which converts different digital speech encoding formatsused between a public telephone network and a radio telephone networkinto compatible ones, e.g. from the format of the fixed network intoanother format of the cellular radio network, and vice versa.

The base transceiver station 204 comprises a control unit 210, amultiplexer unit 212, a base band block 214, a modulator block 216, atransceiver block 218 and an antenna array 240.

The multiplexer unit 212 is used for arranging the traffic and controlchannel used by the transceiver block 218 in reception onto onetransmission connection 211. In transmission, one transmissionconnection 211 is divided between the traffic and control channels usedby the transceiver block 218.

The base band block 214 (BB) includes a digital signal processor, ASICcircuits (application specific integrated circuit), routes, memory meansand software e.g. for encoding and decoding signals, performing errorcorrection functions and possibly for interleaving and deinterleavingbits. In the base band block 214 the complex weighting of antennasignals can also be performed digitally.

The control unit 210 controls the function of the transceiver block 218,base band block 214 and multiplexer 212. The control unit 210determines, for example, antenna weights which are used for weightingand phasing the signals of the antenna array 240 in reception andtransmission.

The antenna array 240 forms a phased antenna array, which comprises atleast two antenna elements 236, 238 for establishing a radio link 250 tothe terminal 170. The antenna elements 236, 238 of the phased antennaarray may constitute a coherent electromagnetic field whose level curvesform a beam-like radiation pattern. In a phased antenna array, thedistance between the antenna elements 236, 238 is typically about halfof the radio wave length used in the radio system, in which case antennabeams can be guided in a sector of ±90° without intra-sectoral phantombeams. The antenna elements 236, 238 can be configured into a linearantenna array (ULA, Uniform Linear Antenna Array), where the phasedifference between the antenna elements 236, 238 depends linearly ontheir location in the antenna array 240 and on the properties of theradio channel, such as the angle dispersion. In a planar manner, it ispossible to form a CA (Circular Array), for example, where the antennaelements are arranged on the same level, e.g. circumferentially andhorizontally. In that case a certain part of the circumference of acircle is covered, e.g. 120 degrees or even the full 360 degrees. Inprinciple, the abovementioned uniplanar antenna structures can also beimplemented as two-dimensional or even as three-dimensional structures.A two-dimensional structure is produced by arranging ULA structures inparallel, for example, in which case the antenna elements form a matrix.The present solution is not restricted to typical linear antenna arraysbut it can also be applied to non-linear and other antenna arrays. Inthis application the antenna elements 236, 238 are denoted by index kwhose values are determined within the following limits 2≦k≦M and M>1.

The antenna array 240 can be used for forming a grid of fixed beams, forexample, where each beam forms a separate area in the coverage area ofthe base station 204. This area may overlap partly or completely withthe other beams.

In addition to the fixed beam method, the phased antenna array can beused for ‘user-specific beamforming’, where the signal of each user isto be transmitted by a narrow beam in the direction of the terminal 170.In the user-specific beamforming, one also tries to follow the movementof the terminal 170. A high data transmission capacity is achieved, thecoverage area of the base station 204 grows and the interference betweenchannels decreases both in the fixed and in the user-specificbeamforming. FIG. 2 further illustrates calibration sensors 242, 244 forcalibrating the antenna array.

FIG. 3 illustrates an example of complex weighting of antenna signals inthe base band block 214 of the base station 204 and of the structure ofthe transceiver block in principle. For the sake of clarity, FIG. 3shows only the transmission sequence of signals, from which a personskilled in the art can easily construe a receiver sequence. Thetransceiver block 218 comprises digital/analogue converters 316A, 318A,316B, 318B for converting signals transmitted from the antenna array 240into analogue form. FIG. 3 further illustrates power amplifiers 322A,322B for amplifying signals to be supplied to the antenna elements 236,238. The transceiver block 218 also comprises frequency converters forupconverting base band signals to the radio frequency, and radiofrequency filters, but these are not shown in FIG. 3. Neither is themodulator block 216 described in greater detail for the sake of clarity.

Complex weighting of antenna signals 302A, 302B shown in FIG. 3 isimplemented by complex multipliers 312A, 314A, 312B, 314B, with whichthe signals 302A, 302B of the base band block can be weighted digitallyaccording to the weights 332A, 334A, 332B, 334B received from thecontrol unit 210, for example. The complex multipliers 312A, 314A, 312A,314B can be implemented by various modulator components, in the signalprocessor of the base band block 214 or by ASIC circuits of the baseband block 214.

Referring to the example shown in FIG. 3, the functional entity formedby the transceiver block 218, modulator block 216 and antenna array 240can be divided into antenna branches 310A, 310B. Each antenna branch310A, 310B comprises at least one antenna element 236, 238 of theantenna array 240 and possibly analogue/digital converters 316A, 318A,316B, 318B, adders 320A, 320B and power amplifiers 322A, 322B. Eachantenna branch 310A, 310B is responsible for processing signals of theantenna elements 236, 238, e.g. weighting, digital/analogue conversion,amplification and filtering. The concept of the present solution isapplicable both to receiving antenna branches and to transmittingantenna branches.

The function of one antenna branch 310A will be described with referenceto FIG. 3. Signals 302A and 302B are supplied to the complex multipliers312A, 312B of the antenna branch 310A and weighted digitally e.g. withweights 332A, 334A produced by the control unit 210 of the basetransceiver station 204 or the radio network controller 146, forinstance. Weighting can be carried out in the base band parts 214 f thebase station 204 e.g. by dividing the signals 302A, 302B into complexand real parts, which are supplied to I and Q branches where the complexand real parts of the signals are weighted separately. This method isknown as IQ multiplication. For the sake of clarity, FIG. 3 illustratesonly one complex multiplier per signal 332A, 334A. After weighting, theweighted signals 302A, 302B are supplied to digital/analogue converters316A, 318A, where they are converted into analogue form. After this, theanalogue signals 302A, 302B are combined in the adder 320A, converted tothe radio frequency in the radio frequency modulator and amplified inthe power amplifier 320A. The amplified signal produced by the poweramplifier 320A is supplied to the antenna element 236, which forms anelectromagnetic component corresponding to weighting in theelectromagnetic field formed by the antenna array 240. The signals 302A,302B can also be weighted by weighting the analogue signal but thisembodiment is not illustrated in FIG. 3. In the weighting of analoguesignals 302A, 302B, the complex multipliers 216 can be placed betweenthe digital/analogue converters 316A, 318A and the power amplifier 324A.In that case the complex multipliers form a ‘phase transmissionnetwork’, which can be controlled digitally. Each signal 302A, 302B tobe weighted is supplied to the input of this network and a weightedsignal is obtained from its output. Weighting can be carried out e.g. bychanging amplification of the weighting amplifier by the weights 332A,334A produced by the control unit 210 of the base station 204. Thecomplex multipliers can also be placed after the power amplifiers 324A,324B, in which case amplification weighting and amplitude weighting areachieved by using a purely analogue phase transmission network. However,also in this case phasing can be controlled digitally. It is obvious toa person skilled in the art that complex weighting can also be carriedout in intermediate frequency parts, which are not shown in FIGS. 2 and3 for the sake of clarity.

FIGS. 3 and 5 illustrate the general principle and mathematicalpresentation of signal weighting and generation of a radiation patternby the antenna array 240. FIG. 5 shows an example of a radiation pattern500 formed by the base station 204, the pattern comprising main beams510-520 and a side lobe structure 530-542. The side lobe structure530-542 is illustrated in a simplified manner: the curve presented by abroken line represents the strongest side beam. The vertical axis 550represents the relative amplitude of the radiation pattern, for example,and the horizontal axis 560 the azimuth angle. The main beams 510-520illustrated in FIG. 5 may be fixed but the present solution is notlimited to fixed; instead, it can be modified according to the user'srequirements and applied to dynamically directed beam structures. Theweighting of antenna signals can be formulated mathematically by meansof weighting factors. In that case the weighting factors are realized asweighting coefficients 332A, 334A, 332B, 334B illustrated in FIG. 3. LetM be the number of antennas 236, 238 in the antenna array 240 and M≧2,and let K be the number of main beams 510-520 formed by the antennaarray 240. Signals to be supplied to different beams 510-520 are denotedby components x_(i), . . . , x_(K) of vector X and weighted signals tobe supplied to different antennas 236, 238 by components y₁,. . . ,y_(M) of vector Y. ThusX=(x ₁ ,x ₂ ,. . . , x _(K))^(T)Y=(y ₁ ,y ₂ , . . ., y _(M))^(T)where index T means transposition of the vector or the matrix. Thefollowing matrix equation is valid for vectors X and YY=VX,where matrix V is the weighting matrix including weighting factors fordifferent antennas 236, 238. The weighting matrix V can be defined asfollows: $V = {\begin{pmatrix}W_{1,1} & W_{1,2} & \cdots & W_{1,K} \\W_{2,1} & W_{2,2} & \cdots & W_{2,K} \\\vdots & \vdots & ⋰ & \vdots \\W_{M,1} & W_{M,2} & \cdots & W_{M,K}\end{pmatrix}.}$

The weighting factors may be relative, in which case they are normalizedto one, i.e. ${\sum\limits_{m = 1}^{M}W_{m,k}^{2}} = 1.$

The weighting coefficients W_(m,k) can be presented in a complex formW_(m,k)(A_(m,k),φ_(m,k))=A_(m,k)e^(iφ) ^(m,k) where A_(m,k) is theamplitude weighting of antenna element k of the antenna array 240 andΦ_(m,k) is the phase factor of antenna element k. The index m refers tothe antenna beam. The phase factor Φ_(m,k) can be an absolute phaseangle or a phase shift in relation to a phase angle of the referenceantenna element. Symbol i is an imaginary unit and e is the Neperfigure. The same amplitude weighting A_(m,k) is often used for allsignals and the desired radiation pattern is formed by means of thephase factors Φ_(m,k). The weighting coefficients W_(m.k) are oftenselected so that orthogonal vectors, by means of which radiationpatterns orthogonal to one another can be achieved, are formed in thematrix V. Orthogonal radiation patterns ensure as small correlation aspossible between the radiation patterns, and thus improve the quality ofdiversity transmission and reception. At the same time the interferencebetween the beams is minimized. The main beams 510-520 narrow as thenumber of antenna elements 236, 238 available increases. In addition,the weighting coefficients W_(m,k) can be selected to realize thedesired window or aperture function. The aperture function can be aGaussian function or another raised cosine function, for example. Theaperture function can be used for adjusting, for example, the dynamicsof the main beam/side lobe structure of the antenna array 240. Here theradiation pattern of antenna array means the radiation pattern used bothin the transmission and in the reception of a radio signal. Theradiation pattern used in the transmission of a radio signal determinesthe signal power of transmission as a function of azimuth angle, whereasin the reception, it determines the receiving sensitivity of the antennaarray as a function of azimuth angle. The radiation pattern of theantenna array can also be utilized in the elevation angle orsimultaneously both in azimuth and elevation angles.

In the case of CDMA-based radio interface applications, beam-specificencoding can be applied to each signal to be transmitted to each mainbeam 510-520 of the radiation pattern 5 illustrated in FIG. 5. In anideal situation, unambiguous encoding corresponds to each main beam510-520 and thus the terminal 170 in the area of each main beam 510-520does not catch signals from other beams. In reality, however, the sidebeams 530-543 interfere with the signals of the main beams 510-520,which reduces the dynamics of the radiation pattern 500.Correspondingly, a beam-specific identification signal, such as a pilotsignal the terminals in the beam area utilize for estimating the radiochannel, for example, can be transmitted to each main beam. Differentbeams may also have partly different coding; for example, the scramblingcode of the CDMA is different in different beams but the channelisationcodes are the same. The identification signal may be any signal thatallows identification of the desired beam. For example, it may be asymbol sequence quence of the TDMA (Time Division Multiple Access)system, which forms a training sequence.

To achieve and maintain the desired beam structure, calibrationoperations can be performed on the antenna branches 310A, 310B.Calibration comprises determination and compensation of amplitude andphase distortion in the antenna branches 310A, 310B so that theamplitudes and phase distortion of the antenna branches 310A, 310B donot exceed their error limits. The need for calibrating the antennaarray 240 typically arises from the fact that components of the antennabranches 310A, 310B, such as power amplifiers 310A, 310B, modulators312A, 314A, 312B, 314B or antenna cables, do not function ideally.Calibration can be performed e.g. using two calibration sensor 242, 244included in the antenna array 240 for measuring the signals 310A, 310Bof the antenna branches. Calibration can also be performed as a routineat regular intervals.

FIG. 4 illustrates a flow chart according to the present solution. Inthe first block 410 the base station may be in any operation mode. Inblock 420 the base station 204 forms a primary radiation pattern 500 byweighting the signals of the M^(th) antenna branch 310A, 310B using theIQ multiplication described above, for example. The primary radiationpattern 500 is formed e.g. by optimizing the weighting factors W_(m,k)when M antenna branches 310A, 310B are used. In the following, theprimary radiation pattern refers to the normal operation of the antennaarray 240 here a desired number M of antenna branches of the antennaarray are in use and they operate normally. The weights that form theprimary radiation pattern 500 are called primary weights, which can bepresented by a primary weighting matrix V_(P).

In block 440 of the chart shown in FIG. 4, N antenna branches 310A, 310Bare disconnected. In an embodiment, a command is formed in accordancewith block 430 shown in FIG. 4 for disconnecting at least one antennabranch 310A, 310B in the base station 204 and the antenna branch 310A,310B concerned is disconnected on the basis of the command formed. Thecommand for disconnecting an antenna branch 310A, 310B can be formed inthe control unit 210 of the base station 204 during calibration, forexample. In that case it may appear that one of the antenna branches310A, 310B cannot be calibrated with sufficient accuracy. This mayresult from a fault in the antenna element, antenna feeding cables orpower amplifiers, for example. The command can also be given when theantenna branches are being serviced. In that case the antenna branch310A, 310B is disconnected and a compensating radiation pattern 700 isused during the service. The command for disconnecting the antennabranch 310A, 310B can also be formed when a power amplifier 322A, 322Breports a failure. The failure report may be given e.g. when onetransistor of a linear power amplifier becomes dysfunctional and thetransmission power of the antenna branch 310A, 310B in questiondecreases, The reason for disconnecting an antenna branch 310A, 310B isnot relevant to the invention as such.

The radiation pattern 600 shown in FIG. 6 illustrates a situation whereone antenna branch 310A, 310B is disconnected but the other functionalantenna branches 310A, 310B continue transmission using the same weightsas earlier. In a common case, the number of disconnected antennabranches 310A, 310B is N, in which case the number of functional antennabranches 310A, 310B is M-N. FIG. 6 illustrates main beams 610-620, and,for the sake of clarity, the side lobe structure 630-640 represents theenvelope of the strongest side beam. The vertical axis 650 representsthe relative amplitude of the radiation pattern, for example, and thehorizontal axis 660 the azimuth angle. In the situation illustrated inFIG. 6, the weights of the functional antenna branches 310A, 310B arenot necessarily optimized to correspond to the M-N antenna branch 310A,310B, and, compared to the primary radiation pattern 500, a clear changeis noticed in the radiation pattern 600. The side lobe structure 630-640has become stronger in relation to the main beams 610-620, which mayresult in a substantial decrease in the capacity of the radio system.

The solution described can be employed for reducing the problems causedby the radiation pattern 600 shown in FIG. 6. In that case, after theantenna branch 310A, 310B has been disconnected, a radiation pattern 700which compensates for the primary radiation pattern 500 is formed inblock 450 of FIG. 4 by weighting the signals of the functional antennabranches 310A, 310B. The signals are weighted by weights whichcompensate for the primary weights and can be presented by a weightingmatrix V^(C). The result is the radiation pattern 700 shown in FIG. 7,where the main beams 710-720 are clearly distinguished from the sidelobe structure 710. The vertical axis 750 represents the relativeamplitude of the radiation pattern, for example, and the horizontal axis760 the azimuth angle. The radiation pattern 700 compensating for theprimary radiation pattern 500 is formed by weighting signals of theantenna branches 310A, 310B to provide the compensating radiationpattern 700 with desired properties. The method ends in block 470 f FIG.4. In that case the base station 204 may continue to function using thecompensating radiation pattern 700. The compensating radiation pattern700 is used until the disconnected antenna branches 310A, 310B arefunctional again. It may also happen that more antenna branches 310A,310B need to be disconnected when the base station transmits using thecompensating radiation pattern 700. In that case the method can beapplied as described above.

In an embodiment, the compensating radiation pattern 700 is formed byweighting signals of functional antenna branches 310A, 310B bypreviously known weights. The previously known weights may be storede.g. in the memory of the control unit 210 or in the memory of the radionetwork controller 146, from which they are loaded into the modulators312A, 314A, 312B, 314B. The previously known weights can be presented bya matrix V^(C) which include the weights, for instance. In that case thecontrol unit 210 of the base station or the radio network controller 146include a number of matrixes V, from which a matrix corresponding to thecurrent compensation case is selected. The compensation case can bedefined on the basis of the functional antenna branches 310A, 310B andthe conditions set on the radiation pattern. A separate identificationnumber, for example, can be allocated to each compensation case. Theelement that stores the compensating weights, such as the control unit210, transmits the weighting coefficients corresponding to thecompensation case to the modulator 216 according to the identificationnumber. The compensation case can be identified in the control unit 210by means of the calibration information or state information on thepower amplifiers, for instance. The calibration information may consistof a calibration report, for example, which shows the accuracy of thecalibration of each antenna branch 310A, 310B. In an embodiment, theprimary radiation pattern 500 is fixed, and thus the compensatingradiation pattern 700 is also fixed. In that case the compensation caseis determined linearly according to a functional antenna configuration.In addition, primary weighting coefficients used for forming the primaryradiation pattern can be employed for identifying the compensation case.The last-mentioned issue is important when one compensates for auser-specific antenna beam whose direction is not pre-determined, andthus the information on disconnected antenna branches 310A, 310B is notnecessarily sufficient for forming the compensating radiation pattern700. In that case a large number of compensating radiation patterns andcorresponding antenna weighting coefficients must be available, fromwhich a suitable one is selected using information obtained on primaryantenna weighting coefficients. This information implicitly includesinformation on the direction of the radiation pattern 500 to becompensated for. A desired number of compensating radiation patterns canbe calculated in advance to achieve the desired directional accuracy.For example, if one wants to direct a transmitting/receiving beam withan accuracy racy of 5 degrees in the direction of the terminal, 24radiation patterns are needed in a sector of 120 degrees, i.e. one foreach feasible direction. The present solution thus enables rapid andcase-specific compensation of a radiation pattern. The terminals 170 inthe area of the base station 204 can operate without interruptionsdespite faults in antennas.

The weighting coefficients that produce the compensating radiationpattern 700 are formed e.g. by simulating radiation patterns and byprocessing the weighting coefficients to provide the radiation patternwith desired properties. The compensating antenna weighting coefficientscan be determined in advance by the manufacturer or the administrator ofthe base station 204, for example. If the disconnected antenna element236, 238 is one of the antenna elements 236, 238 at the edge of theantenna array 240, the compensating radiation pattern 700 can still beformed by primary weighting coefficients. It is particularly demandingto form the compensating radiation pattern 700 when a signal to betransmitted from one of the antenna elements 236, 238 in the middle ofthe antenna array 240 does not fulfill the set conditions and thelinearity of the antenna array disappears. In that case the signals ofthe functional antenna branches 310A, 310B are weighted by compensatingweighting coefficients which differ from the primary weightingcoefficients.

In an embodiment the compensating radiation pattern 700 is formed byweighting signals of the functional antenna branches 310A, 310B withweights which are based on the configuration of the functional antennaelements 236, 238 in the antenna array 240. The antenna configurationcomprises the number of antenna elements 236, 238 in the antenna array240 and their physical positioning. In the selection of antenna weights,one may also consider the radiation pattern formed separately by theantenna elements 236, 238. This radiation pattern depends on the shapeof a single antenna element 236, 238 and on the elements, such asreflectors, close to the antenna element 236, 238. The single antennaelement 236, 238 is a dipole or a rectangular radiation element, knownas a patch antenna. In addition, the aperture weighting function of theantenna array 240 may be taken into account when weights are determined.Case-specific conditions, which depend on the capacity required by acell of the base station 204, can be set on the compensating radiationpattern 700 to be formed. As a general principle, the compensatingradiation pattern 700 should correspond to the primary radiation pattern500 as closely as possible. This situation is achieved relatively easilyif the number of disconnected antenna branches 310A, 310B is smallcompared to the number of functional antenna branches 310A, 310B. Inpractice, however, this is not the case, but disconnection of even oneantenna branch 310A, 310B may have a considerable effect on the qualityof compensation of the primary radiation pattern 500. In that caseproperties that have,priority over the other properties of the radiationpattern can be defined for the compensating radiation pattern 700. Theseproperties include coverage area, number of main beams and dynamic rangeof the radiation pattern.

In an embodiment, the compensating radiation pattern 700 is formed byweighting signals of the functional antenna branches 310A, 310B so thatthe main beams 710-720 of the compensating radiation pattern 700 alwaysoverlap at least partly with the main beams 510-520 of the primaryradiation pattern 500. In that case the radiation pattern 500 and thecompensating radiation pattern 700 will have at least partly the samecoverage area.

In an embodiment, at least one main beam 510-520 of the primaryradiation pattern 500 is compensated with at least one main beam 710-720of the compensating radiation pattern 700. In FIGS. 5 and 7, forexample, main beam 514 of the radiation pattern 500 is compensated withmain beam 714 of the compensating radiation pattern. This case may arisee.g. When a cell in the base station 204 has an area that requires aparticularly high capacity. It is also feasible that each main beam ofthe radiation pattern 500 is compensated with the main beam of thecompensating radiation pattern 700 as follows: main beam 510 with mainbeam 710, main beam 512 with main beam 712, main beam 514 with main beam714, main beam 516 with main beam 716, main beam 518 with main beam 718,and main beam 520 with main beam 720.

In an embodiment, at least one main beam 510-520 of the primaryradiation pattern 500 is compensated with at least one main beam 710-720of the compensating radiation pattern 700 and the coding of the signalsof each compensating main beam 710-720 is the same as the coding of thesignals of the main beam 510-520 to be compensated for. The coding maybe spreading coding of the CDMA-based (Code Division Multiple Access)radio system, which may comprise scrambling and/ or channelisationcoding. In FIGS. 5 and 7, for example, main beam 514 of the radiationpattern 500 is compensated with main beam 714 of the radiation pattern700, and thus the traffic and pilot channels to be transmitted to themain beams 514 and 714 remain unchanged. In that case the terminal 170in the area of the beams 514, 714 in question may continue to functionwithout handover despite the compensation of radiation pattern.

In an embodiment, at least one main beam 710-720 of the primaryradiation pattern 500 is compensated with one main beam 510-520 of thecompensating radiation pattern 700 and the identification signal of thecompensating main beam 710-720 is the same as the identification signalof the main beam (510-520) to be compensated for 500. The identificationsignal may be one of the pilots according to the 3GPP standard, forexample.

In an embodiment, the compensating radiation pattern 700 is formed byweighting the signals of the functional antenna branches so that thedynamic range of the main beams 710-720 in the compensating radiationpattern 700 is optimized. The dynamic range can be optimized byincreasing the amplitude of the main beams 710-720 in the compensatingradiation pattern 700 in relation to the amplitude of the side lobestructure 730 by selecting a suitable weighting function of the antennaarray 240 aperture, for example.

In an embodiment, after the compensating radiation pattern has beenformed, the antenna branches 310A, 310B can also be calibrated accordingto block 460 of FIG. 4 to improve the radiation pattern 700. Calibrationcan be performed as was described above. In an embodiment, the radiationpattern 700 compensating for the primary radiation pattern 500 is formedso that compensation is performed in the azimuth direction. In this casethe antenna array to be used comprises horizontally arrayed antennaelements which are weighted to compensate for the radiation pattern.

In another embodiment, the radiation pattern 700 compensating for theprimary radiation pattern 500 is formed so that compensation isperformed in the elevation direction. In that case, the antenna array tobe used comprises vertically arrayed antenna elements which are weightedto compensate for the radiation pattern.

The above-mentioned instances of compensation in the elevation directionand in the azimuth direction can also be combined, in which case theradiation pattern is compensated in every direction.

The solution described can be applied to reception and transmission in abase station. In an embodiment, the primary radiation pattern 500 is theradiation pattern used in transmission, the disconnected antenna branchis the transmitting antenna branch, and the compensating radiationpattern 700 is the radiation pattern used in transmission.

In another embodiment, the primary radiation pattern 500 is theradiation pattern used in reception, the disconnected antenna branch isthe receiving antenna branch, and the compensating radiation pattern 700is the radiation pattern used in reception. Compensation of thereceiving radiation pattern and weighting of the receiving signals canbe presented e.g. as the block diagram illustrated in FIG. 3 where thedirection of signals has been reversed from antenna arrays 240 tocomplex multipliers 312A, 314A, 312B, 314B. In that case the receivedsignal is weighted in the complex multipliers 312A, 314A, 312B, 314B.Other functions, such as amplification and digital/analogue conversion,are known per se to a person skilled in the art.

A situation where the transmitting antenna branch has been disconnectedwill be described now. If the antenna configuration and the antennaweights used in reception remain unchanged, the receiving radiationpattern will be different from the transmitting radiation pattern. Thissituation may cause problems in the location of terminals and allocationof radio resources to users, for example. In that case signals of thereceiving antenna branches can be re-weighted using a radiation patternin reception that corresponds to the compensating radiation pattern 700used in transmission as closely as possible. The correspondence means,for example, that at least one transmitting antenna beam and onereceiving antenna beam overlap. The new weighting of antennas used inreception can be implemented as follows, for example: one weightingmatrix of a receiving antenna, which is loaded e.g. from the controlunit 210 of the base station, corresponds to each weighting matrix of atransmitting antenna when the transmitting antenna branch isdisconnected. The weighting matrix of the receiving antenna used inreception can be formed by the same methods as the weighting matrix ofthe transmitting antenna. The corresponding function can be performedwhen the antenna branch employed in reception is disconnected and thecompensating radiation pattern is the radiation pattern used inreception. In that case signals of the transmitting antenna branches areweighted as described above so that the radiation pattern used intransmission corresponds to the compensating radiation pattern used inreception.

In an embodiment, the compensating weights used on the downlink and onthe uplink are the same. This embodiment is particularly suitable for aradio interface which employs the TDD technique (Time Division Duplex).In that case, the direction estimate of the terminal 170, for example,can be formed reliably using the same antenna weights of the uplink andthe downlink. However, the above-mentioned method cannot necessarily beapplied in a radio interface based on the FDD technique (FrequencyDivision Duplex) due to the difference in the radio frequency betweenthe uplink and the downlink, i.e. due to a ‘duplex frequency’. In thatcase a separate uplink antenna weighting corresponds to eachcompensating downlink antenna weighting. The uplink antenna weightingcan be formed in the same manner as the downlink antenna weighting usingsimulations.

Even though the invention was described above with reference to theexample according to the accompanying drawings, it is clear that theinvention is not limited to this example, but it may be modified invarious ways within the inventive concept disclosed in the appendedclaims.

1. A method of compensating for a radiation pattern in a radio system,the method comprising: forming a primary radiation pattern by weightingsignals of at least two functional antenna branches of a base station,disconnecting at least one antenna branch; and forming a radiationpattern which compensates for the primary radiation pattern by weightingsignals of the functional antenna branches.
 2. A method of weightingsignals in a radio system, the method comprising: weighting signals ofat least two functional antenna branches of a base station with primaryweights to form a primary radiation pattern, disconnecting at least oneantenna branch; and weighting signals of the functional antenna brancheswith weights which compensate for the primary weights to form acompensating radiation pattern.
 3. A method according to claim 2,further comprising weighting signals of the functional antenna brancheswith previously known weights.
 4. A method according to claim 2, furthercomprising weighting signals of the functional antenna branches withweights which differ from the primary weights.
 5. A method according toclaim 1 or 2, wherein the primary radiation pattern is fixed and thecompensating radiation pattern is fixed.
 6. A method according to claim1 or 2, wherein the primary radiation pattern is the radiation patternused in transmission, the disconnected antenna branch is thetransmitting antenna branch, and the compensating radiation pattern isthe radiation pattern used in transmission.
 7. A method according toclaim 1 or 2, wherein the primary radiation pattern is the radiationpattern used in transmission, the disconnected antenna branch is thetransmitting antenna branch, and the compensating radiation pattern isthe radiation pattern used in transmission; and wherein a radiationpattern which is to be used in reception and corresponds to thecompensating radiation pattern used in transmission is formed byweighting signals of the receiving antenna branches.
 8. A methodaccording to claim 1 or 2, wherein the primary radiation pattern is theradiation pattern used in reception, the disconnected antenna branch isthe receiving antenna branch, and the compensating radiation pattern isthe radiation pattern used in reception.
 9. A method according to claim1 or 2, wherein the primary radiation pattern is the radiation patternused in reception, the disconnected antenna branch is the receivingantenna branch, and the compensating radiation pattern is the radiationpattern used in reception; and wherein a radiation pattern which is tobe used in transmission and corresponds to the compensating radiationpattern used in reception is formed by weighting signals of thetransmitting antenna branches.
 10. A method according to claim 1 or 2,further comprising forming the radiation pattern which compensates forthe primary radiation pattern by weighting signals of the functionalantenna branches so that compensation occurs in the azimuth direction.11. A method according to claim 1 or 2, further comprising forming theradiation pattern compensating for the primary radiation pattern byweighting signals of the functional antenna branches so thatcompensation occurs in the elevation direction.
 12. A method accordingto claim 1 or 2, further comprising forming the compensating radiationpattern by weighting signals of the functional antenna branches withpreviously known weights.
 13. A method according to claim 1, furthercomprising forming the compensating radiation pattern by weightingsignals of the functional antenna branches with weights which differfrom the weights used for forming the primary radiation pattern.
 14. Amethod according to claim 1, further comprising forming the compensatingradiation pattern by weighting signals of the functional antennabranches digitally.
 15. A method according to claim 1, furthercomprising forming the compensating radiation pattern by weightingsignals of the functional antenna branches with weights which are basedon the configuration of the functional antenna elements in the antennaarray.
 16. A method according to claim 1, further comprising forming thecompensating radiation pattern by weighting signals of the functionalantenna branches with weights which are based on the radiation patternsformed by single antenna elements.
 17. A method according to claim 1,further comprising forming the compensating radiation pattern byweighting signals of the functional antenna branches with weights whichare based on the weighting function of the aperture of the antennaarray.
 18. A method according to claim 1, further comprising forming thecompensating radiation pattern by weighting signals of the functionalantenna branches so that the main beams of the compensating radiationpattern overlap at least partly with the main beams of the primaryradiation pattern.
 19. A method according to claim 1, further comprisingforming the compensating radiation pattern by weighting signals of thefunctional antenna branches so that at least one main beam of theprimary radiation pattern is compensated with at least one main beam ofthe compensating radiation pattern.
 20. A method according to claim 1,further comprising forming the compensating radiation pattern byweighting signals of the functional antenna branches so that at leastone main beam of the primary radiation pattern is compensated with onemain beam of the compensating radiation pattern and coding of thesignals of the compensating main beam is the same as the coding of thesignals of the main beam to be compensated for.
 21. A method accordingto claim 1, further comprising forming the compensating radiationpattern by weighting signals of the functional antenna branches so thatat least one main beam of the primary radiation pattern is compensatedwith one main beam of the compensating radiation pattern and theidentification signal of the compensating main beam is the same as theidentification signal of the main beam to be compensated for.
 22. Amethod according to claim 1, further comprising forming the compensatingantenna beam structure by weighting signals of the functional antennabranches so that the dynamic range of the main beams of the compensatingradiation pattern is optimized.
 23. A method according to claim 1,further comprising calibrating the functional antenna branches after thecompensating radiation pattern has been formed.
 24. A method accordingto claim 1, further comprising forming a command for disconnecting atleast one antenna branch; and disconnecting said at least one antennabranch on the basis of the command formed.
 25. A radio systemcomprising: a base station for forming a radio interface of the radiosystem; the base station comprises at least two antenna branches forestablishing a radio link to terminals; each antenna branch comprises atleast one antenna element for forming an antenna array; and the basestation comprises weighting means for weighting signals of thefunctional antenna branches for forming a primary radiation patternwherein the base station is arranged to disconnect at least one antennabranch; and wherein the weighting means are arranged to weight signalsof the functional antenna branches to form a radiation pattern whichcompensates for the primary radiation pattern.
 26. A radio systemaccording to claim 25, wherein the base station is arranged to form afixed primary radiation pattern; and wherein the weighting means arearranged to form a fixed compensating radiation pattern.
 27. A radiosystem according to claim 25, wherein the antenna branches are arrangedto transmit a signal; wherein the weighting means are arranged to weighttransmission signals of the antenna branches; wherein the base stationis arranged to disconnect at least one transmitting antenna branch; andwherein the weighting means are arranged to weight the transmissionsignals of the functional antenna branches to form a radiation patternfor transmission which compensates for the primary radiation patternused for transmission.
 28. A radio system according to claim 25, whereinthe antenna branches are arranged to transmit a signal; wherein theweighting means are arranged to weight transmission signals of theantenna branches; wherein the base station is arranged to disconnect atleast one transmitting antenna branch; wherein the weighting means arearranged to weight transmission signals of the functional antennabranches to form a radiation pattern for transmission which compensatesfor the primary radiation pattern used in transmission; and wherein theweighting means are also arranged to weight receiving signals of theantenna branches so that the radiation pattern for reception correspondsto the compensating radiation pattern used in transmission.
 29. A radiosystem according to claim 25, wherein the antenna branches are arrangedto receive a signal; wherein the weighting means are arranged to weightreception signals of the antenna branches; wherein the base station isarranged to disconnect at least one receiving antenna branch; whereinthe weighting means are arranged to weight reception signals of thefunctional antenna branches to form a radiation pattern for receptionwhich compensates for the primary radiation pattern used in reception;and wherein the weighting means are also arranged to weight transmissionsignals of the functional antenna branches so that the radiation patternformed for transmission corresponds to the compensating radiationpattern used in reception.
 30. A radio system according to claim 25,wherein the weighting means are arranged to weight signals of theantenna branches so that compensation occurs in the azimuth direction.31. A radio system according to claim 25, wherein the weighting meansare arranged to weight signals of the functional antenna branches sothat compensation occurs in the elevation direction.
 32. A radio systemaccording to claim 25, wherein the weighting means are arranged toweight signals of the functional antenna branches with previously knownweights to form the compensating radiation pattern.
 33. A radio systemaccording to claim 25, wherein the weighting means arranged to weightsignals of the functional antenna branches digitally to form acompensating radiation pattern.
 34. A radio system according to claim25, wherein the weighting means are arranged to weight signals of thefunctional antenna branches with weights which are based on theconfiguration of the functional antenna elements in the antenna array35. A radio system according to claim 25, wherein the weighting meansare arranged to weight signals of the functional antenna branches withweights which are based on the radiation patterns formed by singlefunctional antenna elements.
 36. A radio system according to claim 25,wherein the weighting means are arranged to weight signals of thefunctional antenna branches with weights which are based on theweighting function of the aperture in the antenna array.
 37. A radiosystem according to claim 25, wherein the weighting means are arrangedto weight signals of the functional antenna branches so that the mainbeams of the compensating radiation pattern overlap at least partly withthe main beams of the primary radiation pattern.
 38. A radio systemaccording to claim 25, wherein the weighting means arranged to weightsignals of the functional antenna branches so that at least one mainbeam of the primary radiation pattern is compensated with at least onemain beam of the compensating radiation pattern.
 39. A radio systemaccording to claim 25, wherein the weighting means are arranged toweight signals of the functional antenna branches so that at least onemain beam of the primary radiation pattern is compensated with one mainbeam of the compensating radiation pattern and the coding of the signalsof each compensating main beam is the same as the coding of the signalsof the main beam to be compensated for.
 40. A radio system according toclaim 25, wherein the weighting means are arranged to weight signals ofthe functional antenna branches so that at least one main beam of theprimary radiation pattern is compensated with one main beam of thecompensating radiation pattern and the identification signal of eachcompensating main beam is the same as the identification signal of themain beam to be compensated for.
 41. A radio system according to claim25, wherein the weighting means are arranged to weight signals of thefunctional antenna branches so that the dynamic range of the main beamsof the compensating radiation pattern is optimized.
 42. A radio systemaccording to claim 25, wherein the base station comprises means forcalibrating the antenna branches.
 43. A radio system according to claim25, wherein the base station is arranged to form a command fordisconnecting at least one antenna branch; and wherein the base stationis arranged to disconnect said at least one antenna branch on the basisof the command formed.
 44. A base station of a radio system, comprising:at least two antenna branches for establishing a radio link toterminals, each antenna branch comprising at least one antenna elementfor forming an antenna array; weighting means for weighting signals ofthe functional antenna branches for forming a primary radiation pattern,wherein the base station is arranged to disconnect at least one antennabranch; and wherein the weighting means are arranged to weight signalsof the functional antenna branches to form a radiation pattern whichcompensates for the primary radiation pattern.
 45. A base stationaccording to claim 44, wherein the base station is arranged to form afixed primary radiation pattern; and wherein the weighting means arearranged to form a fixed compensating radiation pattern.
 46. A basestation according to claim 44, wherein the antenna branches are arrangedto transmit a signal; wherein the weighting means are arranged to weighttransmission signals of the antenna branches; wherein the base stationis arranged to disconnect at least one transmitting antenna branch; andwherein the weighting means are arranged to weight the transmissionsignals of the functional antenna branches to form a radiation patternfor transmission which compensates for the primary radiation patternused for transmission.
 47. A base station according to claim 44, whereinthe antenna branches are arranged to transmit a signal; wherein theweighting means are arranged to weight transmission signals of theantenna branches; wherein the base station is arranged to disconnect atleast one transmitting antenna branch; wherein the weighting means arearranged to weight transmission signals of the functional antennabranches to form a radiation pattern for transmission which compensatesfor the primary radiation pattern used in transmission; and wherein theweighting means are also arranged to weight receiving signals of theantenna branches so that the radiation pattern for reception correspondsto the compensating radiation pattern used in transmission.
 48. A basestation according to claim 44, wherein the antenna branches are arrangedto receive a signal; wherein the weighting means are arranged to weightreception signals of the antenna branches; wherein the base station isarranged to disconnect at least one receiving antenna branch; whereinthe weighting means are arranged to weight reception signals of thefunctional antenna branches to form a radiation pattern for receptionwhich compensates for the primary radiation pattern used in reception;and wherein the weighting means are also arranged to weight transmissionsignals of the functional antenna branches so that the radiation patternformed for transmission corresponds to the compensating radiationpattern used in reception.
 49. A base station according to claim 44,wherein the weighting means are arranged to weight signals of theantenna branches so that compensation occurs in the azimuth direction.50. A radio system according to claim 44, wherein the weighting meansare arranged to weight signals of the functional antenna branches sothat compensation occurs in the elevation direction.
 51. A base stationaccording to claim 44, wherein the weighting means are arranged toweight signals of the functional antenna branches with previously knownweights to form the compensating radiation pattern.
 52. A base stationaccording to claim 44, wherein the weighting means are arranged toweight signals of the functional antenna branches digitally to form acompensating radiation pattern.
 53. A base station according to claim44, wherein the weighting means are arranged to weight signals of thefunctional antenna branches with weights which are based on theconfiguration of the functional antenna elements in the antenna array.54. A base station according to claim 44, wherein the weighting meansare arranged to weight signals of the functional antenna branches withweights which are based on the radiation patterns formed by singlefunctional antenna elements.
 55. A base station according to claim 44,wherein the weighting means are arranged to weight signals of thefunctional antenna branches with weights which are based on theweighting function of the aperture in the antenna array.
 56. A basestation according to claim 44, wherein the weighting means are arrangedto weight signals of the functional antenna branches so that the mainbeams of the compensating radiation pattern overlap at least partly withthe main beams of the primary radiation pattern.
 57. A base stationaccording to claim 44, wherein the weighting means are arranged toweight signals of the functional antenna branches so that at least onemain beam of the primary radiation pattern is compensated with at leastone main beam of the compensating radiation pattern.
 58. A base stationaccording to claim 44, wherein the weighting means are arranged toweight signals of the functional antenna branches so that at least onemain beam of the primary radiation pattern is compensated with one mainbeam of the compensating radiation pattern and the coding of the signalsof each compensating main beam is the same as the coding of the signalsof the main beam to be compensated for.
 59. A base station according toclaim 44, wherein the weighting means are arranged to weight signals ofthe functional antenna branches so that at least one main beam of theprimary radiation pattern is compensated with one main beam of thecompensating radiation pattern and the identification signal of eachcompensating main beam is the same as the identification signal of themain beam to be compensated for.
 60. A base station according to claim44, wherein the weighting means are arranged to weight signals of thefunctional antenna branches so that the dynamic range of the main beamsof the compensating radiation pattern is optimized.
 61. A base stationaccording to claim 44, wherein the base station comprises means forcalibrating the antenna branches.
 62. A base station according to claim44, wherein the base station is arranged to form a command fordisconnecting at least one antenna branch; and wherein the base stationis arranged to disconnect said at least one antenna branch on the basisof the command formed.